Secure data storage devices encrypt the stored data and include means for controlling access to the data. Without proper authorization, the device does not grant access even to the encrypted data via the storage device interface. However, because physical protection of storage devices is very expensive and in many cases impractical, physical attacks such as disassembling a disc drive and putting the platters on a spin stand with microscopic magnetic detectors, or simply connecting the head signal to another disc controller, could still remain possible. Thus, encryption does not necessarily protect data from modification by an unauthorized party.
When an unauthorized party gains write access to the storage device, he can cause damage, for example by writing back older contents to the same location in the storage medium, or by copying over data from other locations. Since there is no inexpensive physical way to prevent this, a cryptographic method to detect unauthorized changes of the stored data is needed to give a warning to the user that the data has been tampered with.
Traditionally, expensive, fragile physical tamper detectors are employed for this task, like seals on the disc drive enclosure, which tell the user if the drive has been opened.
It would be desirable to provide a tamper detection method that does not rely on physical tamper detectors.